This map seems to contain more information -- world distribution of computers.
Do you think that this can be used to guide me in answering the question: What countries (languages) are worth localization of my software?

You should take a look at http://www.internetworldstats.com/ (warning: 90s design ahead) for some better numbers on internet penetration within different countries. You'd then want to take a look at this list of languages by native speakers, click through on each language to see which countries speak it, and compare that to the penetration of internet usage.

I think you'll find that Spanish is a good start. Hindi too.

Edit: Seeing you mention English in a comment highlights that you're really looking at localization separate from translation. Canada is geographically large, but only has about 28 million internet users (less than Spain), and doesn't have the colonial history of the UK, which despite its mere 47 million internet users, has spread British English throughout the world.

Localizing to British English may be a better first step (and provide an easier learning process for promoting localized software) than translating and localizing to different foreign language markets.

In general, you need to hire a native speaker of each language you want to support to translate the text for your software. If you think this is not necessary and you can do it yourself, take a look at some of the excellent programs produced by Russian programmers for the English market. Many US buyers will not touch these programs because the English in the menus, help files, and documentation is not correct. It makes the product seem amateurish.

So- if your product is still in development, make sure the text is separate from the code and concentrate on English. Don't worry about any other language. Once you are selling the product to the English speaking portions of the world, and those other places that speak both English and some other language, you can look at your sales figures by country. That will tell you what other languages to concentrate on.

If you roll out your product supporting numerous languages all at once you are just going to be wasting your translating dollars.